microRNAs or miRNA refer to short RNAs (19 to 23 nucleotides), which control the expression of different genes. These molecules act as the principle regulators for various biological processes including development, differentiation, proliferation and apoptosis. Therefore, deregulation of miRNAs play an important role in different diseases such as cancer. Therefore, many studies have been performed to investigate miRNA’s biology and function. Many effective efforts have also been performed to promote miRNA’s detection and evaluation procedures. In this article, the biology of miRNA’s in various physiological and pathological processes will be reviewed and a few detection methods for miRNA will be introduced.